Debugger: Fix display of QVariant(QString) inferior call returns

Some versions of GDB seem to be touchy when it comes to casting,
even if the memory contents is the same.

Change-Id: I9733863c20d3726397623fa593063aec0095e774
Reviewed-by: hjk <hjk121@nokiamail.com>

share/qtcreator/debugger/qttypes.py

@@ -2089,7 +2089,7 @@ def qdump__QVariant(d, value):
         if toInteger(value["d"]["is_shared"]):
             val = data["ptr"].cast(innerType.pointer().pointer()).dereference().dereference()
         else:
-            val = data.cast(innerType)
+            val = data["ptr"].cast(innerType)
 
         d.putEmptyValue(-99)
         d.putItem(val)